Stabilizers in photographic emulsions and developers



Patented ar. 11, 1952 STABILIZERS IN PHOTOGRAPHIC EMUL SIGNS ANDDEVELOPERS John David Kendall and Harold Gordon Suggate, Ilford,England, assignors to Ilford Limited, Ilford, England, a British companyNo Drawing. Application August 3, 1949, Serial No. 108,418. In GreatBritain August 6, 1948 density of which bears no relation to thevariations in luminosity of the subject. This overall deposit isreferred to as the chemical fog or development fog. Its effect is toincrease the general density of the negative obtained and to depress thecontrast of the image in the less exposed parts. In general the fogdensity produced is greater in the case of high speed than in slowemulsions and is invariably greater the higher the temperature ofdevelopment and when vigorous developers are used. 'Moreover, the degreeto which an emulsion produces fog on development usually increases withthe age of the emulsion so that photographic materials which have beenkept a long time, especially in warm and humid conditions, or emulsionswhich have been kept a long time in the molten condition, may produceimages associated with a heavy fog density. Many compounds have beensuggested in the past for use as additions to emulsions or to developerswhich tend to reduce the formation of fog, but almost all of them, ifreasonably effective as anti-fogging agents, have caused a seriousreductionin the speed of the photographic emulsion.

According to the present invention the tendency to the formation of fogin silver halide photographic emulsions is reduced by incorporating inthe emulsion or the developer or both a small quantity of a compound ofthe general formula:

Bl l l t.

N N l l periods of time and they enable development to be effected withvigorous developers or at high temperatures. Thus the compounds are ofparticular Value as emulsion or developer additions Claims. (Cl. 957) incases where the emulsions or developers are to be used in tropicalconditions or, in the case of emulsions, where the emulsions are to bekept for a long time in the molten condition. The compounds present thefurther advantage that they do not seriously'reduce the effective speedof emulsions in which they are incorporated.

The new anti-fogging agents may be prepared by the processes describedin our co-pending application Serial No. 108,417, new U. S. Patent No.2,534,914, filed on even date herewith.

As indicated above the group R1 in the general formula may be a hydrogenatom or an alkyl group. Examples of suitable alkyl groups are methyl,ethyl and higher alkyl groups.

The quantity of the compound employed will depend on the emulsion or thedeveloper to which it is added, but as a general indication it may bestated that for incorporation in an emulsion, 1 to 5 or up to 50 cc. ofa 1:1,000 solution of the compound per litre of emulsion is suitable,whilst for incorporation in a developer; the optimum quantity may varyfrom 1 part of the compound in 3,000 to 30,000 parts of the developersolution according to the particular compound used. The addition of thecompound to an emulsion is preferably effected after the digestion ofthe emulsion as a final addition before coating.

The following examples illustrate the invention:

, Examples To an iodobromide emulsion containing 1 /2 gram-molecules ofsilver were added 20 cc. of a 1:1000 ethyl alcohol solution of3.3-bis(1.2.ltriazolyll-formamidine. The emulsion was then coated onglass, dried and stored, part of the product under normal conditions andpart in a sealed container at F. A control emulsion containing nostabiliser was similarly treated. Sensitometric results were as follows:

It will be seen that the emulsion containing the stabiliser gave lessfog than the control on keeping, but without serious effect on the speedformation of fog in silver halide photographic l I H H where R1 isselectiefi frofii theclass consisting of the hydrogen atom ans alkylgroups;

3. A process for red iifg the tendency to the formation of fog in s iver halide photographic emulsions which comprises developing latentimages in such emulsions by means of 9, developing solution containing asmall quantity of a compound of the general formula:

where R1 is selected from the class consisting of the hydrogen atom andalkyl groups, thequantity of the said compound included in the developerbeing equivalent to 1 part of the compound per 3000 to 30,000 parts ofthe developing solution.

4. A process for reducing the tendency to the formation of fog in silverhalide photographic emulsions which comprises developing the emulsions,in the presence of a small quantity of 3.3- bis 1.2.4-tri'a'zolyl)-formamidine.

5. A process for reducing the tendency to the formation of fog in silverhalide photographic emulsions which comprises developing the emulsions,in the presence of a small quantity of 3.3- bis(-methyl-1.2.4-triazolyl) -formamidine.

6. A process for reducing the tendency to the formation of fog in silverhalide photographic emulsions which comprises developing the emulsions,in the presence of a small quantity of 3 .3-bis(5-ethy1-1.2.4-triazolyl)-formamidine.

7. A photographic silverhalide emulsion con-* taining a small quantityof a compound of the general formula:

where R1 is selected from the class consisting of the hydrogen atom andalkyl groups.

8. A photographic silver halide emulsion containing in the proportion of1 to 50 cc. of a 1:1000 5 solution per litre of emulsion a compound ofthe general formula:

where R1 is seltii'd from the class consisting of the hydrogen atom andalkyl groups.

9. A photographic silver halide emulsion containing in the proportion of1 to 50 cc. of a 1:1000 solution per litre of emulsion3.3-bis(1.2.4-triazolyl) -formamidine.

10. A photographic silver halide emulsion containing in the proportionof 1 to 50 cc. of a 1:1000 solution per litre or emulsion3.3-bis(5-methyl- 1 .2.4-triazolyl) -forniamidine.

11. A photographic silver halide emulsion containing in the proportionof 1 to cc. of a 121000 solution per litre of emulsion 3.3-bis(5-ethyl-1.2.4-triazolyl) -formamidihe.

12. .A photographic developing composition including a silver halidephotographic developer and a small quantity of a compound of the generalformulai where R1 is selected from the class consisting of the hydrogenatom and alkyl groups.

13. A photographic developing solution containing a silver halidephotographic developer and, per 3000 to 30,000 parts of the solution, 1part of 3.3'-bis(1.2.4-triazolyl)-formamidine.

14. A photographic developing solution containing a silver halidephotographic developer and, per 3000 to 30,000 parts of the solution, 1part of 3.3-bis(5-methyl-1.2.4-triazolyl)-formamidine.

F0 15. A photographic developing solution containing a silver halidephotographic developer and, per 3000 to 30,000 parts of the solution, 1

part of 3.3'-bis(5-ethyl-1.2.4-triazoly1)-f0rmamidine.

JOHN DAVID KENDALL. HAROLD GORDON SUGGATE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,763,989 Sheppard June 17, 19302,153,930 Kendall Apr. 11, 1939 2,353,754 Peterson July 18, 19442,475,136 Heimbach July 5, 1949 2,476,525 Anish July 19, 1949 2,534,914Kendall Dec. 19, 1950

1. A PROCESS FOR REDUCING THE TENDENCY TO THE FORMATION OF FOG IN SILVERHALIDE PHOTOGRAPHIC EMULSIONS WHICH COMPRISES DEVELOPING THE EMULSIONS,IN THE PRESENCE OF A SMALL QUANTITY OF A COMPOUND OF THE GENERALFORMULA: